Control device for hybrid vehicle

ABSTRACT

Since a supercharging pressure from a supercharger decreases when an actual rotation speed difference is equal to or less than a margin rotation speed difference, a response delay of an engine torque due to a response delay of the supercharging pressure in a high rotation curbing control unit can be appropriately curbed. A shortage of the engine torque with respect to a required engine torque due to a decrease in the supercharging pressure by a supercharging pressure decreasing unit is compensated for using an torque of a second rotary machine. Accordingly, it is possible to curb a decrease in power performance due to a decrease in the supercharging pressure and to prevent an engine rotation speed from falling into a high-rotation state in which the engine rotation speed exceeds a maximum rotation speed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2019-172305 filed on Sep. 20, 2019, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a control device for a hybrid vehicleincluding an engine with a supercharger, a first rotary machine, and asecond rotary machine.

2. Description of Related Art

A hybrid vehicle including (a) an engine, (b) a first rotary machinethat can adjust a rotation speed of the engine, and (c) a second rotarymachine and (d) using the engine and the second rotary machine as drivepower sources is known. An example thereof is a vehicle which isdescribed in Japanese Unexamined Patent Application Publication No.2008-247205 (JP 2008-247205 A). JP 2008-247205 A discloses that theengine and the first rotary machine are controlled such that therotation speed of the engine is within a range which does not exceed amaximum rotation speed which is determined not to exceed predeterminedupper-limit rotation speeds of the engine and the first rotary machineand an output required for the engine is output from the engine.

SUMMARY

Even when the engine and the first rotary machine are controlled in thesame way as in the technique described in JP 2008-247205 A, the enginerotation speed of the engine may increase to be higher than the maximumrotation speed depending on vehicle conditions. In this case, decreasingan output torque of the engine can be considered. However, when theengine includes a supercharger, a response delay of the output torque ofthe engine may occur due to a response delay of a superchargingpressure. Accordingly, even when the engine is controlled such that theoutput torque of the engine is decreased, the rotation speed of theengine may be likely to fall into a high-rotation state in which therotation speed of the engine exceeds the maximum rotation speed as therotation speed of the engine or the first rotary machine becomes closerto the predetermined upper-limit rotation speed thereof.

The present disclosure provides a control device for a hybrid vehiclethat can prevent a rotation speed of an engine from falling into ahigh-rotation state in which the rotation speed of the engine exceeds amaximum rotation speed.

According to a first aspect of the present disclosure, there is provideda control device for (a) a hybrid vehicle including an engine with asupercharger, a first rotary machine that is able to adjust a rotationspeed of the engine, and a second rotary machine and using the engineand the second rotary machine as drive power sources, the control deviceincluding: (b) a high rotation curbing control unit configured tocontrol the engine and the first rotary machine such that an operatingpoint of the engine reaches a target operating point and to control theengine such that an output torque of the engine decreases when therotation speed of the engine exceeds the maximum rotation speed, thetarget operating point being set such that the rotation speed of theengine is within a range which does not exceed a maximum rotation speedwith a margin of the rotation speed of the engine from a predeterminedupper-limit rotation speed of each of the engine and the first rotarymachine and an output required for the engine is output from the engine;(c) a supercharging pressure decreasing unit configured to decrease asupercharging pressure from the supercharger when a speed differencebetween the maximum rotation speed and the rotation speed of the engineis equal to or less than a set margin speed difference; and (d) a torquecompensation unit configured to compensate for a shortage of the outputtorque of the engine with respect to a required engine torque due to adecrease in the supercharging pressure by the supercharging pressuredecreasing unit using a second rotary machine torque of the secondrotary machine.

A second aspect of the present disclosure provides the control devicefor a hybrid vehicle according to the first aspect, wherein thesupercharging pressure decreasing unit is configured to decrease thesupercharging pressure when the shortage of the output torque of theengine with respect to the required engine torque is not able to becompensated for using the second rotary machine torque and the speeddifference is equal to or less than the margin speed difference.

A third aspect of the present disclosure provides the control device fora hybrid vehicle according to the second aspect, wherein thesupercharging pressure decreasing unit is configured to set an amount ofdecrease of the supercharging pressure by the supercharging pressuredecreasing unit to be less when the shortage of the output torque of theengine with respect to the required engine torque is not able to becompensated for using the second rotary machine torque than when theshortage of the output torque of the engine with respect to the requiredengine torque is able to be compensated for using the second rotarymachine torque.

A fourth aspect of the present disclosure provides the control devicefor a hybrid vehicle according to any one of the first to third aspects,further including (a) a condition determining unit configured todetermine whether a vehicle condition is a predetermined vehiclecondition in which the rotation speed of the engine is likely to exceedthe maximum rotation speed, wherein (b) the supercharging pressuredecreasing unit is configured to decrease the supercharging pressurewhen it is determined that the vehicle condition is the predeterminedvehicle condition and the speed difference is equal to or less than themargin speed difference.

A fifth aspect of the present disclosure provides the control device fora hybrid vehicle according to the fourth aspect, wherein the conditiondetermining unit is configured to determine whether the vehiclecondition is the predetermined vehicle condition based on whether thehybrid vehicle is traveling on a road on which driving wheels to whichpower of the engine is transmitted are likely to slip.

A sixth aspect of the present disclosure provides the control device fora hybrid vehicle according to the fourth or fifth aspect, wherein thecondition determining unit is configured to determine whether thevehicle condition is the predetermined vehicle condition based onwhether the first rotary machine is subjected to a predetermined outputlimitation.

The control device for a hybrid vehicle according to the first aspectincludes (b) the high rotation curbing control unit configured tocontrol the engine and the first rotary machine such that the operatingpoint of the engine reaches the target operating point which is set suchthat the rotation speed of the engine is within the range which does notexceed a maximum rotation speed with a margin of the rotation speed ofthe engine from a predetermined upper-limit rotation speed of each ofthe engine and the first rotary machine and the output required for theengine is output from the engine and to control the engine such that theoutput torque of the engine decreases when the rotation speed of theengine exceeds the maximum rotation speed; (c) the superchargingpressure decreasing unit configured to decrease the superchargingpressure from the supercharger when a speed difference between themaximum rotation speed and the rotation speed of the engine is equal toor less than a set margin speed difference; and (d) the torquecompensation unit configured to compensate for a shortage of the outputtorque of the engine with respect to a required engine torque due to adecrease in the supercharging pressure by the supercharging pressuredecreasing unit using a second rotary machine torque of the secondrotary machine. Accordingly, since the supercharging pressure from thesupercharger decreases when the speed difference is equal to or lessthan the margin speed difference, it is possible to appropriately curb aresponse delay of the output torque of the engine due to a responsedelay of the supercharging pressure in the high rotation curbing controlunit. It is possible to compensate for the shortage of the output torqueof the engine with respect to the required engine torque due to thedecrease in the supercharging pressure by the supercharging pressuredecreasing unit using the second rotary machine torque of the secondrotary machine. As a result, it is possible to curb a decrease in powerperformance due to the decrease in the supercharging pressure and toprevent the rotation speed of the engine from falling into ahigh-rotation state in which the rotation speed of the engine exceedsthe maximum rotation speed due to a response delay of the superchargingpressure.

In the control device for a hybrid vehicle according to the secondaspect, the supercharging pressure decreasing unit is configured todecrease the supercharging pressure even when the shortage of the outputtorque of the engine with respect to the required engine torque is notable to be compensated for using the second rotary machine torque andthe speed difference is equal to or less than the margin speeddifference. Accordingly, even when the shortage of the output torque ofthe engine with respect to the required engine torque is not able to becompensated for using the second rotary machine torque, it is possibleto prevent the rotation speed of the engine from falling into ahigh-rotation state in which the rotation speed of the engine exceedsthe maximum rotation speed due to a response delay of the superchargingpressure.

In the control device for a hybrid vehicle according to the thirdaspect, the supercharging pressure decreasing unit is configured to setan amount of decrease of the supercharging pressure by the superchargingpressure decreasing unit to be less when the shortage of the outputtorque of the engine with respect to the required engine torque is notable to be compensated for using the second rotary machine torque thanwhen the shortage of the output torque of the engine with respect to therequired engine torque is able to be compensated for using the secondrotary machine torque. Accordingly, it is possible to curb a decrease inpower performance when the shortage of the output torque of the enginewith respect to the required engine torque is not able to be compensatedfor using the second rotary machine torque.

The control device for a hybrid vehicle according to the fourth aspectfurther includes (a) the condition determining unit configured todetermine whether a vehicle condition is a predetermined vehiclecondition in which the rotation speed of the engine is likely to exceedthe maximum rotation speed, and (b) the supercharging pressuredecreasing unit is configured to decrease the supercharging pressurewhen it is determined that the vehicle condition is the predeterminedvehicle condition and the speed difference is equal to or less than themargin speed difference. Accordingly, since the supercharging pressureis decreased by the supercharging pressure decreasing unit when it isdetermined that the vehicle condition is the predetermined vehiclecondition and the speed difference is equal to or less than the marginspeed difference, it is possible to further curb an excessive decreasein the supercharging pressure, for example, in comparison with a case inwhich the supercharging pressure is decreased when the speed differenceis equal to or less than the margin speed difference.

In the control device for a hybrid vehicle according to the fifthaspect, the condition determining unit determines whether the vehiclecondition is the predetermined vehicle condition based on whether thehybrid vehicle is traveling on a road on which driving wheels to whichpower of the engine is transmitted are likely to slip. Accordingly, itis possible to prevent the rotation speed of the engine from fallinginto a high-rotation state when the hybrid vehicle is traveling on aroad on which the driving wheels are likely to slip.

In the control device for a hybrid vehicle according to the sixthaspect, the condition determining unit determines whether the vehiclecondition is the predetermined vehicle condition based on whether thefirst rotary machine is subjected to a predetermined output limitation.Accordingly, it is possible to appropriately prevent the rotation speedof the engine from falling into a high-rotation state when the firstrotary machine is subjected to the predetermined output limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the present disclosure will be described belowwith reference to the accompanying drawings, in which like numeralsdenote like elements, and wherein:

FIG. 1 is a diagram schematically illustrating a configuration of avehicle to which the present disclosure is applied and illustratingprincipal parts of a control function and a control system for varioustypes of control in the vehicle;

FIG. 2 is a diagram schematically illustrating a configuration of anengine;

FIG. 3 is a collinear diagram relatively illustrating rotation speeds ofrotary elements in a differential unit;

FIG. 4 is a diagram illustrating an example of an optimal engineoperating point;

FIG. 5 is a diagram illustrating an example of a power source switchingmap which is used for switching control between motor-driven travel andhybrid travel;

FIG. 6 is a table illustrating operating states of a clutch and a brakein each travel mode;

FIG. 7 is a diagram illustrating an example of a feasible area of anengine rotation speed;

FIG. 8 is a diagram illustrating an example of a margin rotation speeddifference calculation map which is used to calculate a margin rotationspeed difference;

FIG. 9 is a flowchart illustrating a principal part of a controloperation of an electronic control unit and illustrating a controloperation for preventing a decrease in power performance due to curbingof supercharging by a supercharger and preventing an engine rotationspeed from falling into a high-rotation state in which the enginerotation speed exceeds a maximum rotation speed;

FIG. 10 is a diagram schematically illustrating a configuration of avehicle to which the present disclosure is applied and which isdifferent from the vehicle illustrated in FIG. 1;

FIG. 11 is an operation table illustrating a relationship betweencombinations of a gear shifting operation of a mechanical stepped gearshifting unit illustrated in FIG. 10 and operations of engagementdevices which are used therein;

FIG. 12 is a diagram illustrating an example of a feasible area of anengine rotation speed in the vehicle illustrated in FIG. 10 at a firstAT gear stage;

FIG. 13 is a diagram illustrating an example of a feasible area of anengine rotation speed in the vehicle illustrated in FIG. 10 at a secondAT gear stage;

FIG. 14 is a diagram illustrating an example of a feasible area of anengine rotation speed in the vehicle illustrated in FIG. 10 at a thirdAT gear stage;

FIG. 15 is a diagram illustrating an example of a feasible area of anengine rotation speed in the vehicle illustrated in FIG. 10 at a fourthAT gear stage;

FIG. 16 is a diagram illustrating an example of a timing chart when thecontrol operation illustrated in the flowchart of FIG. 9 is performed inthe vehicle illustrated in FIG. 10.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings.

FIG. 1 is a diagram schematically illustrating a configuration of avehicle 10 to which the present disclosure is applied and illustratingprincipal parts of a control function and a control system for varioustypes of control in the vehicle 10. In FIG. 1, the vehicle 10 is ahybrid vehicle including an engine 12, a first rotary machine MG1, asecond rotary machine MG2, a power transmission device 14, and drivingwheels 16.

FIG. 2 is a diagram schematically illustrating a configuration of theengine 12. In FIG. 2, the engine 12 is a power source for travel of thevehicle 10 and is a known internal combustion engine such as a gasolineengine or a diesel engine including a supercharger 18, that is, anengine with the supercharger 18. An intake pipe 20 is provided in anintake system of the engine 12, and the intake pipe 20 is connected toan intake manifold 22 which is attached to an engine body 12 a. Anexhaust pipe 24 is provided in an exhaust system of the engine 12 andthe exhaust pipe 24 is connected to an exhaust manifold 26 which isattached to the engine body 12 a. The supercharger 18 is a knownexhaust-turbine supercharger, that is, a turbocharger, including acompressor 18 c that is provided in the intake pipe 20 and a turbine 18t that is provided in the exhaust pipe 24. The turbine 18 t isrotationally driven by exhaust gas, that is, a flow of exhaust gas. Thecompressor 18 c is connected to the turbine 18 t and is rotationallydriven by the turbine 18 t to compress air suctioned to the engine 12,that is, intake air.

An exhaust bypass 28 that causes exhaust gas to flow from upstream todownstream with respect to the turbine 18 t by bypassing the turbine 18t is provided in parallel in the exhaust pipe 24. A waste gate valve(=WGV) 30 that continuously controls a ratio of exhaust gas passingthrough the exhaust bypass 28 to exhaust gas passing through the turbine18 t is provided in the exhaust bypass 28. A valve opening of the wastegate valve 30 is continuously adjusted by causing an electronic controlunit (a control unit) 100 which will be described later to operate anactuator which is not illustrated. As the valve opening of the wastegate valve 30 increases, exhaust gas of the engine 12 is more likely tobe discharged via the exhaust bypass 28. Accordingly, in a superchargedstate of the engine 12 in which a supercharging operation of thesupercharger 18 is effective, a supercharging pressure Pchg from thesupercharger 18 decreases as the valve opening of the waste gate valve30 increases. The supercharging pressure Pchg from the supercharger 18is a pressure of intake air and is an air pressure downstream from thecompressor 18 c in the intake pipe 20. A side in which the superchargingpressure Pchg is low is, for example, a side with a pressure of intakeair in a non-supercharged state of the engine 12 in which thesupercharging operation of the supercharger 18 does not work at all,that is, a side with a pressure of intake air in an engine without thesupercharger 18.

An air cleaner 32 is provided in an inlet of the intake pipe 20, and anair flowmeter 34 that measures an amount of intake air Qair of theengine 12 is provided in the intake pipe 20 downstream from the aircleaner 32 and upstream from the compressor 18 c. An intercooler 36which is a heat exchanger that cools intake air compressed by thesupercharger 18 by exchanging heat between intake air and outside air ora coolant is provided in the intake pipe 20 downstream from thecompressor 18 c. An electronic throttle valve 38 of which opening andclosing are controlled by causing the electronic control unit 100 whichwill be described later to operate a throttle actuator which is notillustrated is provided in the intake pipe 20 downstream from theintercooler 36 and upstream from the intake manifold 22. A superchargingpressure sensor 40 that detects the supercharging pressure Pchg from thesupercharger 18 and an intake air temperature sensor 42 that detects anintake air temperature THair which is the temperature of intake air areprovided in the intake pipe 20 between the intercooler 36 and theelectronic throttle valve 38. A throttle valve opening sensor 44 thatdetects a throttle valve opening θth which is an opening of theelectronic throttle valve 38 is provided in the vicinity of theelectronic throttle valve 38, for example, in the throttle actuator.

An air recirculation bypass 46 that causes air to recirculate fromdownstream to upstream with respect to the compressor 18 c by bypassingthe compressor 18 c is provided in parallel in the intake pipe 20. Forexample, an air bypass valve (=ABV) 48 that is opened at the time ofsudden closing of the electronic throttle valve 38 to curb occurrence ofa surge and to protect the compressor 18 c is provided in the airrecirculation bypass 46. A valve opening of the air bypass valve 48 iscontinuously adjusted by causing the electronic control unit 100 whichwill be described later to operate an actuator which is not illustrated.

In the engine 12, an engine torque Te which is an output torque of theengine 12 is controlled by causing the electronic control unit 100 whichwill be described later to control an engine control device 50 (seeFIG. 1) including the electronic throttle valve 38, a fuel injectiondevice, an ignition device, the waste gate valve 30, and the air bypassvalve 48.

Referring back to FIG. 1, the first rotary machine MG1 and the secondrotary machine MG2 are rotary electric machines having a function of anelectric motor (a motor) and a function of a power generator (agenerator) and are so-called motor generators. The first rotary machineMG1 and the second rotary machine MG2 can serve as a power source fortravel of the vehicle 10. The first rotary machine MG1 and the secondrotary machine MG2 are connected to a battery 54 which is provided inthe vehicle 10 via an inverter 52 which is provided in the vehicle 10.In the first rotary machine MG1 and the second rotary machine MG2, anMG1 torque Tg which is an output torque of the first rotary machine MG1and an MG2 torque (a second rotary machine torque) Tm which is an outputtorque of the second rotary machine MG2 are controlled by causing theelectronic control unit 100 which will be described later to control theinverter 52. For example, in the case of forward rotation, an outputtorque of a rotary machine is a powering torque at a positive torquewhich is an acceleration side and is a regenerative torque at a negativetorque which is a deceleration side. The battery 54 is a power storagedevice that transmits and receives electric power to and from the firstrotary machine MG1 and the second rotary machine MG2. The first rotarymachine MG1 and the second rotary machine MG2 are provided in a case 56which is a non-rotary member attached to the vehicle body.

The power transmission device 14 includes a gear shifting unit 58, adifferential unit 60, a driven gear 62, a driven shaft 64, a final gear66, a differential device 68, and a reduction gear 70 in the case 56.The gear shifting unit 58 and the differential unit 60 are arrangedcoaxially with an input shaft 72 which is an input rotary member of thegear shifting unit 58. The gear shifting unit 58 is connected to theengine 12 via the input shaft 72 or the like. The differential unit 60is connected in series to the gear shifting unit 58. The driven gear 62engages with a drive gear 74 which is an output rotary member of thedifferential unit 60. The driven shaft 64 fixes the driven gear 62 andthe final gear 66 such that they cannot rotate relative to each other.The final gear 66 has a smaller diameter than the driven gear 62. Thedifferential device 68 engages with the final gear 66 via a differentialring gear 68 a. The reduction gear 70 has a smaller diameter than thedriven gear 62 and engages with the driven gear 62. A rotor shaft 76 ofthe second rotary machine MG2 which is disposed in parallel to the inputshaft 72 is connected to the reduction gear 70 separately from the inputshaft 72 and is connected to the second rotary machine MG2 in apower-transmittable manner. The power transmission device 14 includes anaxle 78 that is connected to the differential device 68.

The power transmission device 14 having this configuration is suitablyused for a vehicle of a front-engine front-drive (FF) type or arear-engine rear-drive (RR) type. In the power transmission device 14,power which is output from the engine 12, the first rotary machine MG1,and the second rotary machine MG2 is transmitted to the driven gear 62and is transmitted from the driven gear 62 to the driving wheels 16sequentially via the final gear 66, the differential device 68, the axle78, and the like. In this way, the second rotary machine MG2 is a rotarymachine that is connected to the driving wheels 16 in apower-transmittable manner. In the power transmission device 14, theengine 12, the gear shifting unit 58, the differential unit 60, and thefirst rotary machine MG1, and the second rotary machine MG2 are arrangedon different axes, whereby a shaft length is decreased. A reduction gearratio of the second rotary machine MG2 can be set to be great. Power issynonymous with torque or force when not particularly distinguished.

The gear shifting unit 58 includes a first planetary gear mechanism 80,a clutch C1, and a brake B1. The differential unit 60 includes a secondplanetary gear mechanism 82. The first planetary gear mechanism 80 is aknown single-pinion type planetary gear device including a first sungear S1, a first pinion P1, a first carrier CA1 that supports the firstpinion P1 such that it can rotate and revolve, and a first ring gear R1that engages with the first sun gear S1 via the first pinion P1. Thesecond planetary gear mechanism 82 is a known single-pinion typeplanetary gear device including a second sun gear S2, a second pinionP2, a second carrier CA2 that supports the second pinion P2 such that itcan rotate and revolve, and a second ring gear R2 that engages with thesecond sun gear S2 via the second pinion P2.

In the first planetary gear mechanism 80, the first carrier CA1 is arotary element that is integrally connected to the input shaft 72 andconnected to the engine 12 via the input shaft 72 in apower-transmittable manner. The first sun gear S1 is a rotary elementthat is selectively connected to the case 56 via the brake B1. The firstring gear R1 is a rotary element that is connected to the second carrierCA2 of the second planetary gear mechanism 82 which is an input rotarymember of the differential unit 60 and serves as an output rotary memberof the gear shifting unit 58. The first carrier CA1 and the first sungear S1 are selectively connected to each other via the clutch C1.

The clutch C1 and the brake B1 are wet frictional engagement devices andare multi-disc hydraulic frictional engagement devices of whichengagement is controlled by a hydraulic actuator. In the clutch C1 andthe brake B1, operating states such as an engaged state and a disengagedstate are switched based on regulated hydraulic pressures Pc1 and Pb1which are output from a hydraulic pressure control circuit 84 providedin the vehicle 10 by causing the electronic control unit 100 which willbe described later to control the hydraulic pressure control circuit 84provided in the vehicle 10.

In a state in which both the clutch C1 and the brake B1 are disengaged,a differential motion of the first planetary gear mechanism 80 ispermitted. Accordingly, in this state, since a reaction torque of theengine torque Te is not taken in the first sun gear S1, the gearshifting unit 58 is in a neutral state in which mechanical powertransmission is not possible, that is, a neutral state. In a state inwhich the clutch C1 is engaged and the brake B1 is disengaged, therotary elements of the first planetary gear mechanism 80 rotateintegrally. Accordingly, in this state, rotation of the engine 12 istransmitted from the first ring gear R1 to the second carrier CA2 at aconstant speed. On the other hand, in a state in which the clutch C1 isdisengaged and the brake B1 is engaged, rotation of the first sun gearS1 of the first planetary gear mechanism 80 is prohibited and rotationof the first ring gear R1 is increased to be higher than rotation of thefirst carrier CA1. Accordingly, in this state, rotation of the engine 12is increased and output from the first ring gear R1. In this way, thegear shifting unit 58 serves as a two-stage stepped transmission whichis switched, for example, between a low gear stage in a directly coupledstate with a gear ratio of “1.0” and a high gear stage in an overdrivestate with a gear ratio of “0.7.” In a state in which both the clutch C1and the brake B1 are engaged, rotation of the rotary elements of thefirst planetary gear mechanism 80 is prohibited. Accordingly, in thisstate, rotation of the first ring gear R1 which is the output rotarymember of the gear shifting unit 58 is stopped and thus rotation of thesecond carrier CA2 which is the input rotary member of the differentialunit 60 is stopped.

In the second planetary gear mechanism 82, the second carrier CA2 is arotary element that is connected to the first ring gear R1 which is theoutput rotary member of the gear shifting unit 58 and serves as an inputrotary member of the differential unit 60. The second sun gear S2 is arotary element that is integrally connected to the rotor shaft 86 of thefirst rotary machine MG1 and is connected to the first rotary machineMG1 in a power-transmittable manner. The second ring gear R2 is a rotaryelement that is integrally connected to the drive gear 74 and isconnected to the driving wheels 16 in a power-transmittable manner andserves as an output rotary member of the differential unit 60. Thesecond planetary gear mechanism 82 is a power split mechanism thatmechanically splits power of the engine 12 which is input to the secondcarrier CA2 via the gear shifting unit 58 to the first rotary machineMG1 and the drive gear 74. That is, the second planetary gear mechanism82 is a differential mechanism that splits and transmits power of theengine 12 to the driving wheels 16 and the first rotary machine MG1. Inthe second planetary gear mechanism 82, the second carrier CA2 serves asan input element, the second sun gear S2 serves as a reaction element,and the second ring gear R2 serves as an output element. Thedifferential unit 60 constitutes an electrical gear shifting mechanism,for example, an electrical stepless transmission, in which adifferential state of the second planetary gear mechanism 82 iscontrolled by controlling the operating state of the first rotarymachine MG1 along with the first rotary machine MG1 that is connected tothe second planetary gear mechanism 82 in a power-transmittable manner.The first rotary machine MG1 is a rotary machine to which power of theengine 12 is transmitted. Since the gear shifting unit 58 is inoverdrive, an increase in torque of the first rotary machine MG1 iscurbed. Controlling the operating state of the first rotary machine MG1refers to performing operation control of the first rotary machine MG1.

FIG. 3 is a collinear diagram illustrating rotation speeds of the rotaryelements in the differential unit 60 relative to each other. In FIG. 3,three vertical lines Y1, Y2, and Y3 correspond to three rotary elementsof the second planetary gear mechanism 82 constituting the differentialunit 60. The vertical line Y1 represents the rotation speed of thesecond sun gear S2 which is a second rotary element RE2 connected to thefirst rotary machine MG1 (see “MG1” in the drawing). The vertical lineY2 represents the rotation speed of the second carrier CA2 which is afirst rotary element RE1 connected to the engine 12 (see “ENG” in thedrawing) via the gear shifting unit 58. The vertical line Y3 representsthe rotation speed of the second ring gear R2 which is a third rotaryelement RE3 integrally connected to the drive gear 74 (see “OUT” in thedrawing). The second rotary machine MG2 (see “MG2” in the drawing) isconnected to the driven gear 62 engaging with the drive gear 74 via thereduction gear 70 or the like. A mechanical oil pump (see “MOP” in thedrawing) which is provided in the vehicle 10 is connected to the secondcarrier CA2. This mechanical oil pump is operated with rotation of thesecond carrier CA2 to supply oil which is used for engaging operationsof the clutch C1 and the brake B1, lubrication of the parts, and coolingof the parts. When rotation of the second carrier CA2 is stopped, theoil is supplied by an electrical oil pump (not illustrated) which isprovided in the vehicle 10. The gaps between the vertical lines Y1, Y2,and Y3 are determined according to a gear ratio ρ (=number of teeth ofthe sun gear/number of teeth of the ring gear) of the second planetarygear mechanism 82. In the relationship between the vertical axes in thecollinear diagram, when the gap between a sun gear and a carriercorresponds to “1,” the gap between the carrier and a ring gearcorresponds to the gear ratio ρ.

A solid line Lef in FIG. 3 denotes an example of relative speeds of therotary elements at the time of forward travel in a hybrid travel (=HVtravel) mode in which hybrid travel using at least the engine 12 as apower source is possible. A solid line Ler in FIG. 3 denotes an exampleof relative speeds of the rotary elements at the time of reverse travelin the HV travel mode. In the HV travel mode, in the second planetarygear mechanism 82, for example, when an MG1 torque Tg which is areaction torque and a negative torque of the first rotary machine MG1with respect to an engine torque Te that is a positive torque which isinput to the second carrier CA2 via the gear shifting unit 58 is inputto the second sun gear S2, a direct engine-transmitted torque Td whichis a positive torque appears in the second ring gear R2. For example,when the MG1 torque Tg (=−ρ/(1+ρ)×Te) which is a reaction torque withrespect to the engine torque Te that is a positive torque which is inputto the second carrier CA2 is input to the second sun gear S2 in a statein which the clutch C1 is engaged, the brake B1 is disengaged, and thegear shifting unit 58 is in a directly coupled state with a gear ratioof “1.0,” a direct engine-transmitted torque Td (=Te/(1+ρ)=−(1/ρ)×Tg)appears in the second ring gear R2. A combined torque of the directengine-transmitted torque Td and the MG2 torque Tm which are transmittedto the driven gear 62 can be transmitted as a drive torque of thevehicle 10 to the driving wheels 16 according to a required drivingforce. The first rotary machine MG1 serves as a power generator when anegative torque is generated at the time of positive rotation. Agenerated electric power Wg of the first rotary machine MG1 charges thebattery 54 or is consumed in the second rotary machine MG2. The secondrotary machine MG2 outputs the MG2 torque Tm using all or some of thegenerated electric power Wg or electric power from the battery 54 inaddition to the generated electric power Wg. The MG2 torque Tm at thetime of forward travel is a powering torque which is a positive torqueat the time of forward rotation, and the MG2 torque Tm at the time ofreverse travel is a powering torque which is a negative torque at thetime of reverse rotation.

The differential unit 60 can operate as an electrical steplesstransmission. For example, in the HV travel mode, when the rotationspeed of the first rotary machine MG1, that is, the rotation speed ofthe second sun gear S2, increases or decreases with respect to an outputrotation speed No which is the rotation speed of the drive gear 74 whichis constrained on rotation of the driving wheels 16 by controlling theoperating state of the first rotary machine MG1, the rotation speed ofthe second carrier CA2 increases or decreases. Since the second carrierCA2 is connected to the engine 12 via the gear shifting unit 58, anengine rotation speed Ne which is the rotation speed of the engine 12increases or decreases with the increase or decrease in the rotationspeed of the second carrier CA2. Accordingly, in the HV travel, it ispossible to perform control such that an engine operating point OPeng isset to an efficient operating point. This hybrid type is referred to asa mechanical split type or a split type. The first rotary machine MG1 isa rotary machine that can control the engine rotation speed (therotation speed) Ne, that is, a rotary machine that can adjust the enginerotation speed Ne. An operating point is an operation point which isexpressed by a rotation speed and a torque, and the engine operatingpoint OPeng is an operation point of the engine 12 which is expressed bythe engine rotation speed Ne and the engine torque Te.

A dotted line Lm1 in FIG. 3 represents an example of relative speeds ofthe rotary elements at the time of forward travel in asingle-motor-driven EV mode in which motor-driven travel using only thesecond rotary machine MG2 as a power source is possible in amotor-driven travel (=EV travel) mode. A dotted line Lm2 in FIG. 3represents an example of relative speeds of the rotary elements at thetime of forward travel in a two-motor-driven EV mode in whichmotor-driven travel using both the first rotary machine MG1 and thesecond rotary machine MG2 as a power source is possible in the EV travelmode. The EV travel mode is a travel mode in which motor-driven travelusing at least one of the first rotary machine MG1 and the second rotarymachine MG2 as a power source in a state in which operation of theengine 12 is stopped is possible.

In the single-motor-driven EV mode, when both the clutch C1 and thebrake B1 are disengaged and the gear shifting unit 58 falls into aneutral state, the differential unit 60 also falls into a neutral state.In this state, the MG2 torque Tm can be transmitted as a drive torque ofthe vehicle 10 to the driving wheels 16. In the single-motor-driven EVmode, for example, the first rotary machine MG1 is maintained at zerorotation in order to reduce a drag loss in the first rotary machine MG1.For example, even when control is performed such that the first rotarymachine MG1 is maintained at zero rotation, the differential unit 60 isin the neutral state and thus the drive torque is not affected.

In the two-motor-driven EV mode, when both the clutch C1 and the brakeB1 are engaged and rotation of the rotary elements of the firstplanetary gear mechanism 80 is prohibited, the second carrier CA2 isstopped at zero rotation. In this state, the MG1 torque Tg and the MG2torque Tm can be transmitted as the drive torque of the vehicle 10 tothe driving wheels 16.

Referring back to FIG. 1, the vehicle 10 includes an electronic controlunit 100 serving as a controller including the control device for thevehicle 10 associated with control of the engine 12, the first rotarymachine MG1, the second rotary machine MG2, and the like. For example,the electronic control unit 100 is configured to include a so-calledmicrocomputer including a CPU, a RAM, a ROM, and an input and outputinterface, and the CPU performs various types of control of the vehicle10 by performing signal processing in accordance with a program which isstored in the ROM in advance while using a temporary storage function ofthe RAM. The electronic control unit 100 is configured to include acomputer for engine control, a computer for rotary machine control, anda computer for hydraulic pressure control according to necessity.

The electronic control unit 100 is supplied with various signals (forexample, an intake air amount Qair, a supercharging pressure Pchg, anintake air temperature THair, a throttle valve opening θth, an enginerotation speed Ne, an output rotation speed No corresponding to avehicle speed V, wheel speeds Nwdl, Nwdr, Nwsl, and Nwsr which are wheelspeeds Nw of the right and left driving wheels 16 and right and leftdriven wheels which are not illustrated, an MG1 rotation speed Ng whichis the rotation speed of the first rotary machine MG1, an MG2 rotationspeed Nm which is the rotation speed of the second rotary machine MG2,an MG1 temperature THg which is a temperature of the first rotarymachine MG1, for example, a stator temperature, an MG2 temperature THmwhich is a temperature of the second rotary machine MG2, for example, astator temperature, an accelerator opening θacc which is an acceleratoroperation amount by a driver indicating the magnitude of the driver'sacceleration operation, a battery temperature THbat which is atemperature of the battery 54, a battery charging/discharging currentIbat, and a battery voltage Vbat) based on detection values from varioussensors (for example, an air flowmeter 34, a supercharging pressuresensor 40, an intake air temperature sensor 42, a throttle valve openingsensor 44, an engine rotation speed sensor 88, an output rotation speedsensor 90, wheel speed sensors 91, an MG1 rotation speed sensor 92, anMG2 rotation speed sensor 94, an MG1 temperature sensor 95, an MG2temperature sensor 96, an accelerator opening sensor 97, and a batterysensor 98) which are provided in the vehicle 10. The electronic controlunit 100 outputs various command signals (for example, an engine controlcommand signal Se for controlling the engine 12, a rotary machinecontrol command signal Smg for controlling the first rotary machine MG1and the second rotary machine MG2, and a hydraulic pressure controlcommand signal Sp for controlling the operating states of the clutch C1and the brake B1) to various devices (for example, the engine controldevice 50, the inverter 52, the hydraulic pressure control circuit 84,and the wheel brake device 87) which are provided in the vehicle 10.

The electronic control unit 100 calculates a state of charge (SOC) valueSOC [%] which is a value indicating the state of charge of the battery54, for example, based on the battery charging/discharging current Ibatand the battery voltage Vbat. The electronic control unit 100 calculateschargeable and dischargeable powers Win and Wout for defining a feasiblerange of a battery power Pbat which is the power of the battery 54, forexample, based on the battery temperature THbat and the SOC value SOC ofthe battery 54. The chargeable and dischargeable powers Win and Woutinclude a chargeable power Win which is a possible input power fordefining limitation of an input power of the battery 54 and adischargeable power Wout which is a possible output power for defininglimitation of an output power of the battery 54. For example, thechargeable and dischargeable powers Win and Wout decrease as the batterytemperature THbat decreases in a low-temperature area in which thebattery temperature THbat is lower than that in a normal area, anddecreases as the battery temperature THbat increases in ahigh-temperature area in which the battery temperature THbat is higherthan that in the normal area. For example, the chargeable power Windecreases as the SOC value SOC increases in an area in which the SOCvalue SOC is high. For example, the dischargeable power Wout decreasesas the SOC value SOC decreases in an area in which the SOC value SOC islow.

The electronic control unit 100 includes a hybrid control means, thatis, a hybrid control unit 102, that realizes various types of control inthe vehicle 10.

The hybrid control unit 102 has a function of an engine control means,that is, an engine control unit 104, that controls the operation of theengine 12, a function of a rotary machine control means, that is, arotary machine control unit 106, that controls the operations of thefirst rotary machine MG1 and the second rotary machine MG2 via theinverter 52, and a function of a power transmission switching means,that is, a power transmission switching unit 108, that switches a powertransmission state in the gear shifting unit 58, and performs hybriddrive control or the like using the engine 12, the first rotary machineMG1, and the second rotary machine MG2 based on such control functions.

The hybrid control unit 102 calculates a required drive torque Twdemwhich is a drive torque Tw required for the vehicle 10, for example, byapplying the accelerator opening θacc and the vehicle speed V to adriving force map which is a relationship which is acquired and storedin advance by experiment or design, that is, a predeterminedrelationship. In other words, the required drive power Pwdem is arequired drive torque Twdem at the vehicle speed V at that time. Here,the output rotation speed No or the like may be used instead of thevehicle speed V. As the driving force map, for example, a map forforward travel and a map for reverse travel are separately set.

The hybrid control unit 102 outputs an engine control command signal Sewhich is a command signal for controlling the engine 12 and a rotarymachine control command signal Smg which is a command signal forcontrolling the first rotary machine MG1 and the second rotary machineMG2 such that the required drive power Pwdem is realized by at least onepower source of the engine 12, the first rotary machine MG1, and thesecond rotary machine MG2 in consideration of a requiredcharging/discharging power which is a charging/discharging powerrequired for the battery 54 or the like.

For example, when the vehicle travels in the HV travel mode, the enginecontrol command signal Se is a command value of an engine power Pe foroutputting a target engine torque Tetgt at a target engine rotationspeed Netgt in consideration of the optimal engine operating pointOPengf and the like and realizing the required engine power Pedem inconsideration of the required charging/discharging power,charging/discharging efficiency in the battery 54, and the like inaddition to the required drive power Pwdem. The rotary machine controlcommand signal Smg is a command value of a generated electric power Wgof the first rotary machine MG1 that outputs the MG1 torque Tg at theMG1 rotation speed Ng at the time of outputting a command as a reactiontorque for causing the engine rotation speed Ne to reach a target enginerotation speed Netgt and is a command value of power consumption Wm ofthe second rotary machine MG2 that outputs the MG2 torque Tm at the MG2rotation speed Nm at the time of outputting a command. For example, theMG1 torque Tg in the HV travel mode is calculated by feedback control inwhich the first rotary machine MG1 operates such that the enginerotation speed Ne reaches the target engine rotation speed Netgt. Forexample, the MG2 torque Tm in the HV travel mode is calculated such thatthe required drive torque Twdem is acquired by addition to a valuecorresponding to a drive torque Tw based on the enginedirect-transmitted torque Td. The optimal engine operating point OPengfis determined in advance, for example, as an engine operating pointOPeng at which total fuel efficiency in the vehicle 10 is the best inconsideration of charging/discharging efficiency in the battery 54 inaddition to the fuel efficiency of only the engine 12 when the requiredengine power Pedem is realized. The target engine rotation speed Netgtis a target value of the engine rotation speed Ne, that is, a targetrotation speed of the engine 12, and the target engine torque Tetgt is atarget value of the engine torque Te. The engine power Pe is an output,that is, power, of the engine 12 and the required engine power Pedem isan output required for the engine 12. In this way, the vehicle 10 is avehicle in which the MG1 torque Tg which is a reaction torque of thefirst rotary machine MG1 is controlled such that the engine rotationspeed Ne reaches the target engine rotation speed Netgt.

FIG. 4 is a diagram illustrating an example of the optimal engineoperating point OPengf on a two-dimensional coordinate system with theengine rotation speed Ne and the engine torque Te as variables. In FIG.4, a solid line Leng denotes a group of optimal engine operating pointsOPengf. Equi-power lines Lpw1, Lpw2, and Lpw3 denote examples in whichthe required engine power Pedem is required engine powers Pe1, Pe2, andPe3, respectively. A point A is an engine operating point OPengA whenthe required engine power Pe1 is realized on the optimal engineoperating point OPengf, and a point B is an engine operating pointOPengB when the required engine power Pe3 is realized on the optimalengine operating point OPengf. The points A and B are also target valuesof the engine operating point OPeng which is expressed by the targetengine rotation speed Netgt and the target engine torque Tetgt, that is,a target engine operating point OPengtgt which is a target operatingpoint. For example, when the target engine operating point OPengtgtchanges from the point A to the point B with an increase in theaccelerator opening θacc, the engine operating point OPeng is controlledsuch that it changes on a path a passing through the optimal engineoperating points OPengf.

The hybrid control unit 102 selectively sets up the EV travel mode orthe HV travel mode as the travel mode according to the travel conditionsand causes the vehicle 10 to travel in the corresponding travel mode.For example, the hybrid control unit 102 sets up the EV travel mode in amotor-driven travel area in which the required drive power Pwdem is lessthan a predetermined threshold value, and sets up the HV travel mode ina hybrid travel area in which the required drive power Pwdem is equal toor greater than the predetermined threshold value. Even when therequired drive power Pwdem is in the motor-driven travel area, thehybrid control unit 102 sets up the HV travel mode when the SOC valueSOC of the battery 54 is less than a predetermined engine startthreshold value or when warming-up of the engine 12 is necessary. Theengine start threshold value is a predetermined threshold value fordetermining whether the SOC value SOC indicates that the battery 54needs to be charged by forcibly starting the engine 12.

FIG. 5 is a diagram illustrating an example of a power source switchingmap which is used for switching control between motor-driven travel andhybrid travel. In FIG. 5, a solid line Lswp is a boundary line betweenthe motor-driven travel area and the hybrid travel area at whichswitching between the motor-driven travel and the hybrid travel isperformed. An area in which the vehicle speed V is relatively low, therequired drive torque Twdem is relatively small, and the required drivepower Pwdem is relatively small is defined in advance in themotor-driven travel area. An area in which the vehicle speed V isrelatively high, the required drive torque Twdem is relatively great,and the required drive power Pwdem is relatively great is defined inadvance in the hybrid travel area. When the SOC value SOC of the battery54 is less than the engine-start threshold value or when warming-up ofthe engine 12 is necessary, the motor-driven travel area in FIG. 5 maybe changed to the hybrid travel area.

When the EV travel mode is set up and the required drive power Pwdem canbe realized by only the second rotary machine MG2, the hybrid controlunit 102 sets up a single-motor-driven EV mode. On the other hand, whenthe EV travel mode is set up and the required drive power Pwdem cannotbe realized by only the second rotary machine MG2, the hybrid controlunit 102 sets up a two-motor-driven EV mode. Although the required drivepower Pwdem can be realized by only the second rotary machine MG2, thehybrid control unit 102 may set up the two-motor-driven EV mode when useof both the first rotary machine MG1 and the second rotary machine MG2is more efficient than use of only the second rotary machine MG2.

The hybrid control unit 102 controls engagements of the clutch C1 andthe brake B1 based on the set-up travel mode. The hybrid control unit102 outputs a hydraulic pressure control command signal Sp for engagingand/or disengaging the clutch C1 and the brake B1 to the hydraulicpressure control circuit 84 such that transmission of power for travelin the set-up travel mode becomes possible.

FIG. 6 is a table illustrating operating states of the clutch C1 and thebrake B1 in the travel modes. In FIG. 6, mark O denotes engagement ofthe clutch C1 and the brake B1, a blank denotes disengagement, and markΔ denotes that one thereof is engaged at the time of additional use ofan engine brake for switching the engine 12 in a rotation-stopped stateto a corotating state. “G” denotes that the first rotary machine MG1serves mainly as a generator, and “M” denotes that the first rotarymachine MG1 and the second rotary machine MG2 serve mainly as a motor atthe time of driving and serve mainly as a generator at the time ofregeneration. The vehicle 10 can selectively realize the EV travel modeand the HV travel mode as a travel mode. The EV travel mode has twomodes including the single-motor-driven EV mode and the two-motor-drivenEV mode.

The single-motor-driven EV mode is realized in a state in which both theclutch C1 and the brake B1 are disengaged. In the single-motor-driven EVmode, the clutch C1 and the brake B1 are disengaged and thus the gearshifting unit 58 falls into a neutral state. When the gear shifting unit58 falls into the neutral state, the differential unit 60 falls into aneutral state in which a reaction torque of the MG1 torque Tg is nottaken in the second carrier CA2 connected to the first ring gar R1. Inthis state, the hybrid control unit 102 causes the second rotary machineMG2 to output the MG2 torque Tm for travel (see a dotted line Lm1 inFIG. 3). In the single-motor-driven EV mode, reverse travel may beperformed by rotating the second rotary machine MG2 oppositely to therotating direction at the time of forward travel.

In the single-motor-driven EV mode, since the first ring gear R1 iscorotated with the second carrier CA2 but the gear shifting unit 58 isin the neutral state, the engine 12 is not corotated but is stopped withzero rotation. Accordingly, when regeneration control is performed inthe second rotary machine MG2 during travel in the single-motor-drivenEV mode, it is possible to take a large amount of regeneration. When thebattery 54 is fully charged and regenerative energy is not taken duringtravel in the single-motor-driven EV mode, use of the engine brake incombination can be considered. When the engine brake is used together,the brake B1 or the clutch C1 is engaged (see “USE IN COMBINATION WITHENGINE BRAKE” in FIG. 6). When the brake B1 or the clutch C1 is engaged,the engine 12 is corotated and the engine brake operates.

The two-motor-driven EV mode is realized in a state in which both theclutch C1 and the brake B1 are engaged. In the two-motor-driven EV mode,since the clutch C1 and the brake B1 are engaged, rotation of the rotaryelements of the first planetary gear mechanism 80 is stopped, the engine12 is stopped with zero rotation, and rotation of the second carrier CA2connected to the first ring gear R1 is stopped. When rotation of thesecond carrier CA2 is stopped, a reaction torque of the MG1 torque Tg istaken in the second carrier CA2, and thus the MG1 torque Tg can bemechanically output from the second ring gear R2 and be transmitted tothe driving wheels 16. In this state, the hybrid control unit 102 causesthe first rotary machine MG1 and the second rotary machine MG2 to outputthe MG1 torque Tg and the MG2 torque Tm for travel (see the dotted lineLm2 in FIG. 3). In the two-motor-driven EV mode, both the first rotarymachine MG1 and the second rotary machine MG2 can be rotated oppositelyto the rotating direction at the time of forward travel to allow reversetravel.

A low state of the HV travel mode is realized in a state in which theclutch C1 is engaged and the brake B1 is disengaged. In the low state ofthe HV travel mode, since the clutch C1 is engaged, the rotary elementsof the first planetary gear mechanism 80 are integrally rotated and thegear shifting unit 58 falls into a directly coupled state. Accordingly,rotation of the engine 12 is transmitted from the first ring gear R1 tothe second carrier CA2 at a constant speed. A high state of the HVtravel mode is realized in a state in which the brake B1 is engaged andthe clutch C1 is disengaged. In the high state of the HV travel mode,since the brake B1 is engaged, rotation of the first sun gear S1 isstopped and the gear shifting unit 58 falls into an overdrive state.Accordingly, rotation of the engine 12 increases and is transmitted fromthe first ring gear R1 to the second carrier CA2. In the HV travel mode,the hybrid control unit 102 causes the first rotary machine MG1 tooutput the MG1 torque Tg which is a reaction torque of the engine torqueTe by power generation and causes the second rotary machine MG2 tooutput the MG2 torque Tm by the generated electric power Wg of the firstrotary machine MG1 (see a solid line Lef in FIG. 3). In the HV travelmode, for example, in the low state of the HV travel mode, the secondrotary machine MG2 can also be rotated oppositely to the rotatingdirection at the time of forward travel to allow reverse travel (see asolid line Ler in FIG. 3). In the HV travel mode, the vehicle can traveladditionally using the MG2 torque Tm based on electric power from thebattery 54. In the HV travel mode, for example, when the vehicle speed Vis relatively high and the required drive torque Twdem is relativelysmall, the high state of the HV travel mode is set up.

Here, the hybrid control unit 102 controls the engine 12 and the firstrotary machine MG1 such that the engine rotation speed Ne does notexceed an upper-limit engine rotation speed Nelim and the MG1 rotationspeed Ng does not exceed an upper-limit MG1 rotation speed Nglim. Theupper-limit engine rotation speed Nelim is, for example, a predeterminedupper-limit rotation speed for making it difficult to decrease theperformance of the engine 12, which is defined as a predetermined ratingof the engine 12. The upper-limit MG1 rotation speed Nglim is, forexample, a predetermined upper-limit rotation speed for making itdifficult to decrease the performance of the first rotary machine MG1,which is defined as a predetermined rating of the first rotary machineMG1. Since the engine rotation speed Ne or the MG1 rotation speed Ng isassociated with each other as can be clearly understood from thecollinear diagram illustrated in FIG. 3, the MG1 rotation speed Ng canbe made not to exceed the upper-limit MG1 rotation speed Nglim inaddition to the engine rotation speed Ne, for example, by defining afeasible area of the engine rotation speed Ne.

FIG. 7 is a diagram illustrating an example of a feasible area of theengine rotation speed Ne on a two-dimensional coordinate system with thevehicle speed V and the engine rotation speed Ne as variables. In FIG.7, when the engine rotation speed Ne increases in a low area of thevehicle speed, that is, the output rotation speed No, the MG1 rotationspeed Ng exceeds the upper-limit MG1 rotation speed Nglim before theengine rotation speed Ne exceeds the upper-limit engine rotation speedNelim, and thus a feasible area of the engine rotation speed Ne isdefined according to the upper-limit MG1 rotation speed Nglim. As thevehicle speed V increases, the feasible area of the engine rotationspeed Ne which is defined according to the upper-limit MG1 rotationspeed Nglim is enlarged to a high-rotation side of the engine rotationspeed Ne. However, since a predetermined upper-limit rotation speed isdefined in the engine 12, the feasible area of the engine rotation speedNe is defined according to the upper-limit engine rotation speed Nelimin a middle vehicle-speed area. On the other hand, when the outputrotation speed No increases in the low area of the engine rotation speedNe, a relative rotation speed Np2 of the second pinion P2 which is theabsolute value of a rotation speed difference between an autorotationspeed of the second pinion P2 and the rotation speed of the secondcarrier CA2 corresponding to the engine rotation speed Ne, that is, arevolution speed of the second pinion P2 increases and thus the feasiblearea of the engine rotation speed Ne is defined according to anupper-limit rotation speed of the relative rotation speed of the secondpinion P2. The upper-limit rotation speed of the relative rotation speedof the second pinion P2 is, for example, a predetermined upper-limitrotation speed for making it difficult to decrease the performance ofthe second pinion P2. As the engine rotation speed Ne increases, thefeasible area of the engine rotation speed Ne which is defined accordingto the upper-limit rotation speed of the relative rotation speed of thesecond pinion P2 is enlarged to a high vehicle-speed side. However,since a predetermined upper-limit rotation speed is defined in thesecond rotary machine MG2, the feasible area of the engine rotationspeed Ne is defined according to an upper-limit MG2 rotation speed Nmlimin a high vehicle-speed area. The upper-limit MG2 rotation speed Nmlimis, for example, a predetermined upper-limit rotation speed for makingit difficult to decrease the performance of the second rotary machineMG2, which is defined as a predetermined rating of the second rotarymachine MG2.

When the engine rotation speed Ne does not exceed the upper-limitrotation speed in the feasible area of the engine rotation speed Ne asillustrated in FIG. 7, the engine rotation speed Ne cannot exceed theupper-limit engine rotation speed Nelim and the MG1 rotation speed Ngcannot exceed the upper-limit MG1 rotation speed Nglim. In thisembodiment, in order for the engine rotation speed Ne not to exceed theupper-limit engine rotation speed Nelim and in order for the MG1rotation speed Ng not to exceed the upper-limit MG1 rotation speedNglim, the hybrid control unit 102 more appropriately performs controlsuch that the engine rotation speed Ne is within a range which is notgreater than a maximum rotation speed Nemax of the engine rotation speedNe set lower by a margin α than the upper-limit rotation speed in thefeasible area of the engine rotation speed Ne. The margin α is, forexample, a margin of the engine rotation speed Ne which is determined inadvance such that the engine rotation speed Ne and the MG1 rotationspeed Ng do not exceed the predetermined upper-limit rotation speedsthereof. Since the engine 12 is controlled within a range which is notgreater than the maximum rotation speed Nemax, the first rotary machineMG1 is controlled within a range which is not greater than a maximumrotation speed Ngmax of the MG1 rotation speed Ng which is set to belower by a margin β than the upper-limit MG1 rotation speed Nglim. Themargin β is, for example, a margin of the MG1 rotation speed Ng which isdetermined in advance such that the MG1 rotation speed Ng does notexceed the upper-limit MG1 rotation speed Nglim.

The above-mentioned target engine operating point OPengtgt is set as anengine operating point OPeng for realizing the required engine powerPedem, and is set in consideration that the engine rotation speed Ne iswithin a range which is not greater than the maximum rotation speedNemax. The hybrid control unit 102 serves as a high rotation curbingcontrol means, that is, a high rotation curbing control unit 110, thatcontrols the engine 12 and the first rotary machine MG1 such that theengine operating point OPeng reaches the target engine operating pointOPengtgt which is set such that the engine rotation speed Ne is within arange not greater than the maximum rotation speed Nemax with a margin(=margin α) of the engine rotation speed Ne from the predeterminedupper-limit rotation speeds of the engine 12 and the first rotarymachine MG1 and which is set such that the required engine power Pedemis output from the engine 12. Control of the engine 12 is, for example,control of the engine torque Te for outputting the target engine torqueTetgt. Control of the first rotary machine MG1 is, for example, controlof the MG1 torque Tg by feedback control for operating the first rotarymachine MG1 such that the engine rotation speed Ne reaches the targetengine rotation speed Netgt.

The engine rotation speed Ne may increase to exceed the maximum rotationspeed Nemax depending on a vehicle condition. In this case, decreasingthe engine torque Te can be considered. However, since the engine 12includes the supercharger 18, the engine rotation speed Ne may be morelikely to fall into a high-rotation state as the engine rotation speedNe or the MG1 rotation speed Ng approaches a predetermined upper-limitrotation speed thereof due to a response delay of the superchargingpressure Pchg even when the engine 12 is controlled such that the enginetorque Te is decreased. Therefore, in order to prevent the enginerotation speed Ne from falling into a high-rotation state in which theengine rotation speed Ne exceeds the maximum rotation speed Nemax, thehybrid control unit 102 decreases the supercharging pressure Pchg whenan actual rotation speed difference ΔN [rpm] which is a speed differencebetween the maximum rotation speed Nemax and the engine rotation speedNe is equal to or less than a margin rotation speed difference (a marginspeed difference) ΔNr [rpm].

Specifically, in order to realize a control function of curbing adecrease in power performance due to curbing of supercharging by thesupercharger 18 and preventing the engine rotation speed Ne from fallinginto a high-rotation state in which the engine rotation speed Ne exceedsthe maximum rotation speed Nemax, the electronic control unit 100includes a supercharging pressure decreasing means, that is, asupercharging pressure decreasing unit 104 a, in the engine control unit104 and the electronic control unit 100 further includes a torquecompensation means, that is, a torque compensation unit 106 a, in therotary machine control unit 106. The electronic control unit 100 furtherincludes a condition determining means, that is, a condition determiningunit 112. The condition determining unit 112 determines whether theengine rotation speed Ne exceeds the maximum rotation speed Nemax.

When the condition determining unit 112 determines that the enginerotation speed Ne exceeds the maximum rotation speed Nemax, the highrotation curbing control unit 110 controls the engine 12 such that theengine torque Te decreases. The high rotation curbing control unit 110decreases the engine torque Te, for example, by performing at least onetorque-down control of decreasing an opening of the electronic throttlevalve 38 and delaying an ignition time. Alternatively, the high rotationcurbing control unit 110 decreases the engine torque Te, for example, byperforming fuel-cut control for stopping supply of fuel to the engine12.

The condition determining unit 112 determines whether the vehiclecondition is a predetermined vehicle condition in which the enginerotation speed Ne is likely to exceed the maximum rotation speed Nemax.

When the vehicle travels on a road on which the driving wheels 16 islikely to slip, that is, a slippery road, the output rotation speed Nois likely to increase due to idling of the driving wheels 16 and theengine rotation speed Ne is also likely to increase. Alternatively, whenthe vehicle is traveling on a road on which the driving wheels 16 arelikely to slip, the output rotation speed No is likely to decrease dueto lock of the driving wheels 16 and the MG1 rotation speed Ng is alsolikely to increase. The slippery road is a road on which the drivingwheels 16 are likely to idle or to be locked and examples thereofinclude a low-μ road, a rough road, and an unpaved road.

The condition determining unit 112 determines whether the vehiclecondition is the predetermined vehicle condition based on whether thevehicle 10 is traveling on a road on which the driving wheels 16 arelikely to slip. The condition determining unit 112 determines whetherthe vehicle 10 is traveling on a road which the driving wheels 16 arelikely to slip, for example, based on whether a difference between anaverage wheel speed Nwd of the wheel speeds Nwdl and Nwdr of the drivingwheels 16 and an average wheel speed Nws of the wheel speeds Nwsl andNwsr of the driven wheels is greater than a predetermined slipdetermination threshold value for determining whether a tire slip hasoccurred. Alternatively, it may be determined whether the vehicle 10 istraveling on a road which the driving wheels 16 are likely to slip usinga wheel slip rate SR (=(Nwd−Nws)/Nwd), rates of change of the wheelspeeds Nwdl, Nwdr, Nwsl, and Nwsr, an outside air temperature, a roadsurface temperature, vehicle acceleration, and the like.

The supercharging pressure decreasing unit 104 a includes a decreasecondition satisfaction determining means, that is, a decrease conditionsatisfaction determining unit 104 b, and a decrease amount calculatingmeans, that is, a decrease amount calculating unit 104 c. When thedecrease condition satisfaction determining unit 104 b determines that asupercharging pressure decrease condition CD has been satisfied, thesupercharging pressure decreasing unit 104 a decreases the superchargingpressure Pchg by setting a target supercharging pressure Pchgtgt [kPa]which is a target value of the supercharging pressure Pchg from thesupercharger 18 to be lower by an amount of decrease PD [kPa] calculatedby the decrease amount calculating unit 104 c. The engine control unit104 outputs an engine control command signal Se for controlling thevalve opening of the waste gate valve 30 to the engine control device 50such that the actual supercharging pressure Pchg reaches the targetsupercharging pressure Pchgtgt.

When a preset first condition CD1 and a preset second condition CD2 areboth satisfied, the decrease condition satisfaction determining unit 104b determines that the supercharging pressure decrease condition CD hasbeen satisfied. The first condition CD1 is satisfied, for example, whenthe condition determining unit 112 determines that the vehicle conditionis the predetermined vehicle condition. The second condition CD2 issatisfied, for example, when the actual rotation speed difference ΔN isequal to or less than the margin rotation speed difference ΔNr (ΔN≤ΔNR).

The actual rotation speed difference ΔN is a speed difference(Nemax1−Ne1) between a maximum rotation speed Nemax1 [rpm] and an enginerotation speed Ne1 [rpm]. The maximum rotation speed Nemax1 is, forexample, a maximum rotation speed Nemax of the engine rotation speed Newhich is set to be lower by a margin α than an upper-limit rotationspeed at a vehicle speed V1 [km/h] which is detected by the outputrotation speed sensor 90 when the condition determining unit 112determines that the vehicle condition is the predetermined vehiclecondition in the feasible area of the engine rotation speed Neillustrated in FIG. 7. The engine rotation speed Ne1 is, for example, anengine rotation speed Ne which is detected by the engine rotation speedsensor 88 when the condition determining unit 112 determines that thevehicle condition is the predetermined vehicle condition. The marginrotation speed difference ΔNr is calculated, for example, using a marginrotation speed difference calculation map illustrated in FIG. 8. In themargin rotation speed difference calculation map, the margin rotationspeed difference ΔNr is set to increase as a margin between the enginerotation speed Ne during travel and the maximum rotation speed Nemaxdecreases, and the margin rotation speed difference ΔNr is set todecrease as the margin increases. The margin can be expressed, forexample, by a friction coefficient μ of a road on which the vehicle istraveling. As the friction coefficient μ decreases, the engine rotationspeed Ne is likely to increase and thus the margin decreases. As thefriction coefficient μ increases, the engine rotation speed Ne is lesslikely to increase and thus the margin increases. The frictioncoefficient μ of a road may be expressed by a wheel slip rate SR. Whenthe friction coefficient μ of a road is expressed by the wheel slip rateSR, the friction coefficient μ of the road decreases as the wheel sliprate SR increases and the friction coefficient μ of the road increasesas the wheel slip rate SR decreases. The friction coefficient μ of aroad or the wheel slip rate SR is calculated, for example, using thewheel speeds Nwdl, Nwdr, Nwsl, and Nwsr which are detected by the wheelspeed sensors 91 when the condition determining unit 112 determines thatthe vehicle condition is the predetermined vehicle condition.

The torque compensation unit 106 a includes an assist possibilitydetermining means, that is, an assist possibility determining unit 106b. When the decrease condition satisfaction determining unit 104 bdetermines that the supercharging pressure decrease condition CD hasbeen satisfied, the assist possibility determining unit 106 b determineswhether compensation (assistance) for a shortage of the engine torque Tewith respect to the required engine torque due to a decrease in thesupercharging pressure Pchg by the supercharging pressure decreasingunit 104 a is able to be performed using the MG2 torque Tm of the secondrotary machine MG2, for example, based on a dischargeable power Wout andthe MG2 temperature THm.

When a preset third condition CD3 is satisfied, the torque compensationunit 106 a compensates for the shortage of the engine torque Te withrespect to the required engine torque due to a decrease in thesupercharging pressure Pchg by the supercharging pressure decreasingunit 104 a using the MG2 torque Tm of the second rotary machine MG2. Thethird condition CD3 is satisfied, for example, when the assistpossibility determining unit 106 b determines that the shortage of theengine torque Te is able to be compensated for using the MG2 torque Tmof the second rotary machine MG2 and the supercharging pressure Pchg isdecreased by the supercharging pressure decreasing unit 104 a. Forexample, when the supercharging pressure Pchg is decreased by thesupercharging pressure decreasing unit 104 a and the assist possibilitydetermining unit 106 b determines that the shortage of the engine torqueTe is not able to be compensated for using the MG2 torque Tm of thesecond rotary machine MG2, the torque compensation unit 106 a does notcompensate for the shortage of the engine torque Te with respect to therequired engine torque due to a decrease in the supercharging pressurePchg using the MG2 torque Tm of the second rotary machine MG2. That is,when the torque compensation unit 106 a is not able to compensate forthe shortage of the engine torque Te with respect to the required enginetorque due to a decrease in the supercharging pressure Pchg by thesupercharging pressure decreasing unit 104 a using the MG2 torque Tm ofthe second rotary machine MG2 and it is determined that thesupercharging pressure decrease condition CD has been satisfied, thesupercharging pressure decreasing unit 104 a decreases the superchargingpressure Pchg.

When the assist possibility determining unit 106 b determines whetherthe shortage of the engine torque Te is able to be compensated for usingthe MG2 torque Tm of the second rotary machine MG2, the decrease amountcalculating unit 104 c calculates an amount of decrease PD [kPa]. Forexample, when the assist possibility determining unit 106 b determinesthat the shortage of the engine torque Te is able to be compensated forusing the MG2 torque Tm of the second rotary machine MG2, the decreaseamount calculating unit 104 c calculates a preset first amount ofdecrease PD1 [kPa]. When the assist possibility determining unit 106 bdetermines that the shortage of the engine torque Te is not able to becompensated for using the MG2 torque Tm of the second rotary machineMG2, the decrease amount calculating unit 104 c calculates a presetsecond amount of decrease PD2 [kPa]. The first amount of decrease PD1 isset to an amount of decrease PD which is greater than the second amountof decrease PD2 (PD1>PD2). That is, the supercharging pressuredecreasing unit 104 a sets an amount of decrease by which thesupercharging pressure Pchg is decreased, that is, an amount of decreasePD by which the target supercharging pressure Pchgtgt is decreased, tobe less when the assist possibility determining unit 106 b determinesthat the shortage of the engine torque Te is not able to be compensatedfor using the MG2 torque Tm of the second rotary machine MG2 than whenthe assist possibility determining unit 106 b determines that theshortage of the engine torque Te is able to be compensated for using theMG2 torque Tm of the second rotary machine MG2.

FIG. 9 is a flowchart illustrating a principal part of a controloperation of the electronic control unit 100 and illustrating a controloperation for curbing a decrease in power performance due to curbing ofsupercharging by the supercharger 18 and preventing the engine rotationspeed Ne from falling into a high-rotation state in which the enginerotation speed Ne exceeds the maximum rotation speed Nemax.

In FIG. 9, first, in Step (the word “step” is omitted below) S10corresponding to the functions of the decrease condition satisfactiondetermining unit 104 b and the condition determining unit 112, it isdetermined whether the vehicle 10 is traveling on a road on which thedriving wheels 16 are likely to slip, for example, whether the vehicle10 is traveling on a low-μ road. When the determination result of S10 ispositive, that is, when the vehicle 10 is traveling on a road on whichthe driving wheels 16 are likely to slip, S20 corresponding to thefunction of the decrease condition satisfaction determining unit 104 bis performed. When the determination result of S10 is negative, that is,when the vehicle 10 is not traveling on a road on which the drivingwheels 16 are likely to slip and the supercharging pressure decreasecondition CD has not been satisfied, S30 corresponding to the functionof the hybrid control unit 102 is performed. In S20, the actual rotationspeed difference ΔN which is a speed difference between the maximumrotation speed Nemax1 and the engine rotation speed Ne1 is calculated.Then, S40 corresponding to the function of the decrease conditionsatisfaction determining unit 104 b is performed. In S40, the marginrotation speed difference ΔNr is calculated, for example, using themargin rotation speed difference calculation map illustrated in FIG. 8.Then, S50 corresponding to the function of the decrease conditionsatisfaction determining unit 104 b is performed. In S50, it isdetermined whether the actual rotation speed difference ΔN is greaterthan the margin rotation speed difference ΔNr (ΔN>ΔNr). When thedetermination result of S50 is positive, that is, when the actualrotation speed difference ΔN is not equal to nor less than the marginrotation speed difference ΔNr and the supercharging pressure decreasecondition CD has not been satisfied, S30 is performed. When thedetermination result of S50 is negative, that is, when the actualrotation speed difference ΔN is equal to or less than the marginrotation speed difference ΔNr and the supercharging pressure decreasecondition CD has been satisfied, S60 corresponding to the function ofthe assist possibility determining unit 106 b is performed. In S30, thesupercharging pressure Pchg is not decreased and a ratio (a torqueratio) between output torques of the engine 12 and the second rotarymachine MG2 which are drive power sources is not changed.

In S60, it is determined whether the shortage of the engine torque Tewith respect to the required engine torque due to a decrease in thesupercharging pressure Pchg is able to be compensated for using the MG2torque Tm of the second rotary machine MG2, that is, whether torqueassist using the second rotary machine MG2 is possible. When thedetermination result of S60 is positive, that is, when the shortage ofthe engine torque Te with respect to the required engine torque due to adecrease in the supercharging pressure Pchg is able to be compensatedfor using the MG2 torque Tm, S70 corresponding to the function of thedecrease amount calculating unit 104 c and the supercharging pressuredecreasing unit 104 a is performed. When the determination result of S60is negative, that is, when the shortage of the engine torque Te withrespect to the required engine torque due to a decrease in thesupercharging pressure Pchg is not able to be compensated for using theMG2 torque Tm, S80 corresponding to the function of the decrease amountcalculating unit 104 c and the supercharging pressure decreasing unit104 a is performed. In S70, the target supercharging pressure Pchgtgt isset to be lower by the first amount of decrease PD1 and thus thesupercharging pressure Pchg is decreased. In S80, the targetsupercharging pressure Pchgtgt is set to be lower by the second amountof decrease PD2 and thus the supercharging pressure Pchg is decreased.Then, S90 corresponding to the function of the torque compensation unit106 a is performed. In S90, the shortage of the engine torque Te withrespect to the required engine torque due to a decrease in thesupercharging pressure Pchg is compensated for using the MG2 torque Tmof the second rotary machine MG2. That is, in S90, torque assist usingthe second rotary machine MG2 is performed.

According to this embodiment described above, the control device for ahybrid vehicle includes: the high rotation curbing control unit 110 thatcontrols the engine 12 and the first rotary machine MG1 such that theengine operating point OPeng reaches the target engine operating pointOPengtgt which is set such that the engine rotation speed Ne is withinthe range which does not exceed the maximum rotation speed Nemax with amargin of the engine rotation speed Ne from a predetermined upper-limitrotation speed of each of the engine 12 and the first rotary machine MG1and the output required for the engine 12 is output from the engine 12and controls the engine 12 such that the engine torque Te decreases whenthe engine rotation speed Ne exceeds the maximum rotation speed Nemax;the supercharging pressure decreasing unit 104 a that decreases thesupercharging pressure Pchg from the supercharger 18 when the speeddifference between the maximum rotation speed Nemax and the enginerotation speed Ne, that is, the actual rotation speed difference ΔN, isequal to or less than the margin rotation speed difference ΔNr; and thetorque compensation unit 106 a that compensates for a shortage of theengine torque Te with respect to a required engine torque due to adecrease in the supercharging pressure Pchg by the superchargingpressure decreasing unit 104 a using the MG2 torque Tm of the secondrotary machine MG2. Accordingly, since the supercharging pressure Pchgfrom the supercharger 18 decreases when the actual rotation speeddifference ΔN is equal to or less than the margin rotation speeddifference ΔNr, it is possible to appropriately curb a response delay ofthe engine torque Te due to a response delay of the superchargingpressure Pchg in the high rotation curbing control unit 110. It ispossible to compensate for the shortage of the engine torque Te withrespect to the required engine torque due to the decrease in thesupercharging pressure Pchg by the supercharging pressure decreasingunit 104 a using the MG2 torque Tm of the second rotary machine MG2. Asa result, it is possible to curb a decrease in power performance due tothe decrease in the supercharging pressure Pchg and to prevent theengine rotation speed Ne from falling into a high-rotation state inwhich the engine rotation speed Ne exceeds the maximum rotation speedNemax due to a response delay of the supercharging pressure Pchg.

According to this embodiment, the supercharging pressure decreasing unit104 a decreases the supercharging pressure Pchg when the shortage of theengine torque Te with respect to the required engine torque is not ableto be compensated for using the MG2 torque Tm and the actual rotationspeed difference ΔN is equal to or less than the margin rotation speeddifference ΔNr. Accordingly, even when the shortage of the engine torqueTe with respect to the required engine torque is not able to becompensated for using the MG2 torque Tm, it is possible to prevent theengine rotation speed Ne from falling into a high-rotation state inwhich the engine rotation speed Ne exceeds the maximum rotation speedNemax due to a response delay of the supercharging pressure Pchg.

According to this embodiment, the supercharging pressure decreasing unit104 a sets an amount of decrease by which the supercharging pressurePchg is decreased by the supercharging pressure decreasing unit 104 a tobe less when the shortage of the engine torque Te with respect to therequired engine torque is not able to be compensated for using the MG2torque Tm than when the shortage of the engine torque Te with respect tothe required engine torque is able to be compensated for using the MG2torque Tm. Accordingly, it is possible to appropriately curb a decreasein power performance when the shortage of the engine torque Te withrespect to the required engine torque is not able to be compensated forusing the MG2 torque Tm.

According to this embodiment, the control device further includes thecondition determining unit 112 that determines whether the vehiclecondition is a predetermined vehicle condition in which the enginerotation speed Ne is likely to exceed the maximum rotation speed Nemax,and the supercharging pressure decreasing unit 104 a decreases thesupercharging pressure Pchg when it is determined that the vehiclecondition is the predetermined vehicle condition and actual rotationspeed difference ΔN is equal to or less than the margin rotation speeddifference ΔNr. Accordingly, since the supercharging pressure Pchg isdecreased by the supercharging pressure decreasing unit 104 a when it isdetermined that the vehicle condition is the predetermined vehiclecondition and the actual rotation speed difference ΔN is equal to orless than the margin rotation speed difference ΔNr, it is possible tofurther curb an excessive decrease in the supercharging pressure Pchg,for example, in comparison with a case in which the superchargingpressure Pchg is decreased when the actual rotation speed difference ΔNis equal to or less than the margin rotation speed difference ΔNr.

According to this embodiment, the condition determining unit 112determines whether the vehicle condition is the predetermined vehiclecondition based on whether the vehicle 10 is traveling on a road onwhich the driving wheels 16 to which power of the engine 12 istransmitted are likely to slip. Accordingly, it is possible to preventthe engine rotation speed Ne from falling into a high-rotation statewhen the vehicle 10 is traveling on a road on which the driving wheels16 are likely to slip.

Another embodiment of the present disclosure will be described below. Inthe following description, elements common to those in theabove-mentioned embodiment will be referred to by the same referencesigns and description thereof will not be repeated.

In this embodiment, a vehicle 200 which is different from the vehicle 10described above in the first embodiment and which is illustrated in FIG.10 is exemplified. FIG. 10 is a diagram schematically illustrating aconfiguration of a vehicle 200 to which the present disclosure isapplied. In FIG. 10, the vehicle 200 is a hybrid vehicle including anengine 202, a first rotary machine MG1, a second rotary machine MG2, apower transmission device 204, driving wheels 206.

The engine 202, the first rotary machine MG1, and the second rotarymachine MG2 have the same configurations as the engine 12, the firstrotary machine MG1, and the second rotary machine MG2 described above inthe first embodiment. An engine torque Te of the engine 202 iscontrolled by causing an electronic control unit 240 which will bedescribed later to control an engine control device 208 including anelectronic throttle valve, a fuel injection device, an ignition device,and a waste gate valve which are provided in the vehicle 200. The firstrotary machine MG1 and the second rotary machine MG2 are connected to abattery 212 that is a power storage device provided in the vehicle 200via an inverter 210 provided in the vehicle 200. An MG1 torque Tg and anMG2 torque Tm of the first rotary machine MG1 and the second rotarymachine MG2 are controlled by causing the electronic control unit 240 tocontrol the inverter 210.

A power transmission device 204 includes an electrical stepless gearshifting unit 216 and a mechanical stepped gear shifting unit 218 whichare arranged in series on a common axis in a case 214 that is anon-rotary member attached to the vehicle body. The electrical steplessgear shifting unit 216 is connected to the engine 202 directly orindirectly via a damper which is not illustrated or the like. Themechanical stepped gear shifting unit 218 is connected to an output sideof the electrical stepless gear shifting unit 216. The powertransmission device 204 includes a differential gear unit 222 that isconnected to an output shaft 220 which is an output rotary member of themechanical stepped gear shifting unit 218 and a pair of axles 224 thatis connected to the differential gear unit 222 or the like. In the powertransmission device 204, power which is output from the engine 202 orthe second rotary machine MG2 is transmitted to the mechanical steppedgear shifting unit 218 and is transmitted from the mechanical steppedgear shifting unit 218 to the driving wheels 206 via the differentialgear unit 222 or the like. The power transmission device 204 having thisconfiguration is suitably used for a vehicle of a front-enginerear-drive (FR) type. In the following description, the electricalstepless gear shifting unit 216 is referred to as a stepless gearshifting unit 216 and the mechanical stepped gear shifting unit 218 isreferred to as a stepped gear shifting unit 218. The stepless gearshifting unit 216, the stepped gear shifting unit 218, or the like isdisposed to be substantially symmetric with respect to the common axis,and a lower half with respect to the axis is not illustrated in FIG. 10.The common axis is an axis of a crankshaft of the engine 202, aconnection shaft 226 connected to the crankshaft, or the like.

The stepless gear shifting unit 216 includes a differential mechanism230 that is a power split mechanism that mechanically splits power ofthe engine 202 to the first rotary machine MG1 and an intermediatetransmission member 228 which is an output rotary member of the steplessgear shifting unit 216. The first rotary machine MG1 is a rotary machineto which power of the engine 202 is transmitted. The second rotarymachine MG2 is connected to the intermediate transmission member 228 ina power-transmittable manner. Since the intermediate transmission member228 is connected to the driving wheels 206 via the stepped gear shiftingunit 218, the second rotary machine MG2 is a rotary machine that isconnected to the driving wheels 206 in a power-transmittable manner. Thedifferential mechanism 230 is a differential mechanism that splits andtransmits power of the engine 202 to the driving wheels 206 and thefirst rotary machine MG1. The stepless gear shifting unit 216 is anelectrical stepless transmission in which a differential state of thedifferential mechanism 230 is controlled by controlling the operatingstate of the first rotary machine MG1. The first rotary machine MG1 is arotary machine that can control an engine rotation speed Ne, that is,adjust the engine rotation speed Ne.

The differential mechanism 230 is constituted by a single-pinion typeplanetary gear unit and includes a sun gear S0, a carrier CA0, and aring gear R0. The engine 202 is connected to the carrier CA0 via theconnection shaft 226 in a power-transmittable manner, the first rotarymachine MG1 is connected to the sun gear S0 in a power-transmittablemanner, and the second rotary machine MG2 is connected to the ring gearR0 in a power-transmittable manner. In the differential mechanism 230,the carrier CA0 serves as an input element, the sun gear S0 serves as areaction element, and the ring gear R0 serves as an output element.

The stepped gear shifting unit 218 is a stepped transmissionconstituting a part of a power transmission path between theintermediate transmission member 228 and the driving wheels 206, thatis, a mechanical gear shifting mechanism constituting a part of a powertransmission path between the stepless gear shifting unit 216 (which issynonymous with the differential mechanism 230) and the driving wheels206. The intermediate transmission member 228 also serves as an inputrotary member of the stepped gear shifting unit 218. The stepped gearshifting unit 218 is, for example, a known planetary gear type automatictransmission including a plurality of planetary gear units such as afirst planetary gear unit 232 and a second planetary gear unit 234 and aplurality of engagement devices such as a one-way clutch F1, a clutchC1, a clutch C2, a brake B1, and a brake B2. In the followingdescription, the clutch C1, the clutch C2, the brake B1, and the brakeB2 are simply referred to as engagement devices CB when not particularlydistinguished.

Each engagement device CB is a hydraulic frictional engagement devicewhich is constituted by a multi-disc or single-disc clutch or brakewhich is pressed by a hydraulic actuator, a band brake which istightened by a hydraulic actuator, and the like. The operating statesuch as an engaged state or a disengaged state of each engagement deviceCB is switched by changing an engagement torque Tcb which is a torquecapacity thereof using controlled engagement oil pressures PRcb of theengagement devices CB which are output from solenoid valves SL1 to SL4or the like in a hydraulic pressure control circuit 236 provided in thevehicle 200.

In the stepped gear shifting unit 218, rotary elements of the firstplanetary gear unit 232 and the second planetary gear unit 234 arepartially connected to each other directly or indirectly via theengagement devices CB or the one-way clutch F1 or are connected to theintermediate transmission member 228, the case 214, or the output shaft220. The rotary elements of the first planetary gear unit 232 are afirst sun gear S1, a first carrier CAL and a first ring gear R1, and therotary elements of the second planetary gear unit 234 are a second sungear S2, a second carrier CA2, and a second ring gear R2.

In the stepped gear shifting unit 218, one gear stage of a plurality ofgear stages with different gear ratios γat (=AT input rotation speedNi/AT output rotation speed Noat) is formed by engaging one of aplurality of engagement devices. In this embodiment, a gear stage whichis formed in the stepped gear shifting unit 218 is referred to as an ATgear stage. The AT input rotation speed Ni is an input rotation speed ofthe stepped gear shifting unit 218 and has the same value as a rotationspeed of the intermediate transmission member 228 and the same value asan MG2 rotation speed Nm. The AT output rotation speed No is a rotationspeed of the output shaft 220 which is an output rotation speed of thestepped gear shifting unit 218 and is also an output rotation speed of acomposite transmission 238 which is a combined transmission includingthe stepless gear shifting unit 216 and the stepped gear shifting unit218.

In the stepped gear shifting unit 218, for example, as illustrated in anengagement operation table of FIG. 11, four forward AT gear stagesincluding a first AT gear stage (“1st” in the drawing) to a fourth ATgear stage (“4th” in the drawing) are formed as a plurality of AT gearstages. The gear ratio γat of the first AT gear stage is the highest andthe gear ratio γat becomes lower in a higher AT gear stage. A reverse ATgear stage (“Rev” in the drawing) is formed, for example, by engagementof the clutch C1 and engagement of the brake B2. That is, for example,the first AT gear stage is formed at the time of reverse travel. Theengagement operation table illustrated in FIG. 11 is obtained bycollecting relationships between the AT gear stages and the operationstates of the plurality of engagement devices. In FIG. 11, “O” denotesengagement, “A” denotes engagement at the time of engine braking or atthe time of coast downshift of the stepped gear shifting unit 218, and ablank denotes disengagement.

In the stepped gear shifting unit 218, an AT gear stage which is formedaccording to a driver's operation of an accelerator, a vehicle speed V,or the like is switched, that is, a plurality of AT gear stages areselectively formed, by an electronic control unit 240 which will bedescribed later. For example, in gear shifting control of the steppedgear shifting unit 218, so-called clutch-to-clutch gear shifting inwhich gear shifting is performed by switching one of the engagementdevices CB, that is, gear shifting is performed by switching of theengagement device CB between engagement and disengagement, is performed.

The vehicle 200 further includes an one-way clutch F0. The one-wayclutch F0 is a lock mechanism that can fix the carrier CA0 in anon-rotatable manner. That is, the one-way clutch F0 is a lock mechanismthat can fix the connection shaft 226 which is connected to thecrankshaft of the engine 202 and which rotates integrally with thecarrier CA0 to the case 214. In the one-way clutch F0, one member of twomembers rotatable relative to each other is integrally connected to theconnection shaft 226 and the other member is integrally connected to thecase 214. The one-way clutch F0 idles in a positive rotating directionwhich is a rotating direction at the time of operation of the engine 202and is automatically engaged in a negative rotating direction which isopposite to that at the time of operation of the engine 202.Accordingly, at the time of idling of the one-way clutch F0, the engine202 is rotatable relative to the case 214. On the other hand, at thetime of engagement of the one-way clutch F0, the engine 202 is notrotatable relative to the case 214. That is, the engine 202 is fixed tothe case 214 by engagement of the one-way clutch F0. In this way, theone-way clutch F0 permits rotation in the positive rotating direction ofthe carrier CA0 which is a rotating direction at the time of operationof the engine 202 and prohibits rotation in the negative rotatingdirection of the carrier CA0. That is, the one-way clutch F0 is a lockmechanism that can permit rotation in the positive rotating direction ofthe engine 202 and prohibit rotation in the negative rotating direction.

The vehicle 200 further includes an electronic control unit 240 which isa controller including a control device for the vehicle 200 associatedwith control of the engine 202, the first rotary machine MG1, the secondrotary machine MG2, and the like. The electronic control unit 240 hasthe same configuration as the electronic control unit 100 describedabove in the first embodiment. The electronic control unit 240 issupplied with various signals which are the same as supplied to theelectronic control unit 100. Various command signals which are the sameas output from the electronic control unit 100 are output from theelectronic control unit 240. The electronic control unit 240 hasfunctions equivalent to the functions of the hybrid control unit 102,and the condition determining unit 112 which are included in theelectronic control unit 100. The electronic control unit 240 can realizea control function capable of curbing a decrease in power performancedue to curbing of supercharging by the supercharger and preventing ahigh-rotation state in which the engine rotation speed Ne exceeds themaximum rotation speed Nemax, which is the same function as realized bythe electronic control unit 100 described above in the first embodiment.

In the vehicle 200, the stepped gear shifting unit 218 is provided inseries on the rear stage of the stepless gear shifting unit 216.Accordingly, when the AT gear stage of the stepped gear shifting unit218 is switched at a certain vehicle speed V, the rotation speed of thering gear R0 which is the output rotation speed of the stepless gearshifting unit 216 changes. Then, a feasible area of the engine rotationspeed Ne changes based on a difference between the AT gear stages in thestepped gear shifting unit 218.

FIGS. 12, 13, 14, and 15 are diagrams illustrating an example of afeasible area of the engine rotation speed Ne on a two-dimensionalcoordinate system with the vehicle speed V and the engine rotation speedNe as variables and illustrating an embodiment other than illustrated inFIG. 7 in the first embodiment. FIG. 12 illustrates a case in which thestepped gear shifting unit 218 is set to the first AT gear stage, FIG.13 illustrates a case in which the stepped gear shifting unit 218 is setto the second AT gear stage, FIG. 14 illustrates a case in which thestepped gear shifting unit 218 is set to the third AT gear stage, andFIG. 15 illustrates a case in which the stepped gear shifting unit 218is set to the fourth AT gear stage. In FIGS. 12, 13, 14, and 15, thebasic idea for defining the feasible area of the engine rotation speedNe is the same as described above with reference to FIG. 7. As thestepped gear shifting unit 218 is set to a higher AT gear stage at acertain vehicle speed V, the rotation speed of the ring gear R0 which isthe output rotation speed of the stepless gear shifting unit 216 becomeslower. Accordingly, in a low area of the engine rotation speed Ne, thefeasible area of the engine rotation speed Ne which is defined accordingto the upper limit of the relative rotation speed of the second pinionP2 is enlarged to a higher vehicle speed side at a higher AT gear stage.At the third AT gear stage or at the fourth AT gear stage, the rotationspeed of the ring gear R0 decreases and thus the feasible area of theengine rotation speed Ne is not defined according to the upper-limit MG2rotation speed Nmlim, but the feasible area of the engine rotation speedNe is defined according to a maximum vehicle speed of the vehicle 200.When the AT gear stage of the stepped gear shifting unit 218 is on ahigh side and the rotation speed of the ring gear R0 decreases, the MG1rotation speed Ng is likely to increase. Accordingly, in a low vehiclespeed area, limitation on a high rotation side of the feasible area ofthe engine rotation speed Ne which is defined according to theupper-limit MG1 rotation speed Nglim increases as the AT gear stagebecomes higher.

FIG. 16 is a diagram illustrating an example of a timing chart when thecontrol operation illustrated in the flowchart of FIG. 9 according tothe first embodiment is performed in the vehicle 200. FIG. 16 is adiagram illustrating an example in which it is determined that thevehicle 200 is traveling on a road on which the driving wheels 206 arelikely to slip due to slippage of the driving wheels 206 and thesupercharging pressure Pchg is decreased. In FIG. 16, time point t1indicates a time point at which the driving wheels 206 slip and it isdetermined that the vehicle 200 is traveling on a road on which thedriving wheels 206 are likely to slip (determination of slippage). Timepoint t2 indicates a time point at which the actual rotation speeddifference ΔN becomes equal to or less than the margin rotation speeddifference ΔNr and it is determined that the supercharging pressuredecrease condition CD for decreasing the supercharging pressure Pchg hasbeen satisfied (determination of the supercharging pressure decreasecondition satisfaction). In this embodiment, by this determination ofthe supercharging pressure decrease satisfaction condition, thesupercharging pressure Pchg is decreased to decrease the engine torqueTe and the MG2 torque Tm of the second rotary machine MG2 is increasedsuch that a shortage of the engine torque Te with respect to a requiredengine torque due to the decrease in the supercharging pressure Pchg isable to be compensated. Accordingly, in this embodiment, it is possibleto achieve the same advantage as in the first embodiment of curbing adecrease in power performance due to the decrease in the superchargingpressure Pchg and preventing the engine rotation speed Ne from fallinginto a high-rotation state in which the engine rotation speed Ne exceedsthe maximum rotation speed Nemax due to a response delay of thesupercharging pressure Pchg.

While embodiments of the present disclosure have been described above indetail with reference to the accompanying drawings, the presentdisclosure can also be applied to other aspects.

For example, in the first embodiment, the condition determining unit 112determines whether the vehicle condition is the predetermined vehiclecondition based on whether the vehicle 10 is traveling on a road onwhich the driving wheels 16 are likely to slip. For example, thecondition determining unit 112 may determine whether the vehiclecondition is the predetermined vehicle condition based on whether thefirst rotary machine MG1 is subjected to a predetermined outputlimitation. The predetermined output limitation is, for example, anoutput limitation with which power generation or powering by the firstrotary machine MG1 at the time of outputting of the MG1 torque Tg whichis a reaction torque of the engine torque Te cannot be appropriatelyperformed. When the first rotary machine MG1 is subjected to thepredetermined output limitation, control of the first rotary machine MG1for causing the engine rotation speed Ne to reach the target enginerotation speed Netgt may not be appropriately performed and the enginerotation speed Ne is likely to increase. Examples of the outputlimitation with which power generation or powering by the first rotarymachine MG1 cannot be appropriately performed include a state in whichthe temperature of the first rotary machine MG1 is high or low such thatthe MG1 temperature THg departs from a predetermined normal temperaturearea THgra and a state in which the temperature of the battery 54 ishigh or low such that the battery temperature THbat departs from apredetermined normal temperature area THbatra. The predetermined normaltemperature area THgra is a normal use area of the first rotary machineMG1 and is a predetermined temperature area of the first rotary machineMG1 in which the output of the first rotary machine MG1 does notdecrease according to the MG1 temperature THg. The predetermined normaltemperature area THbatra is a normal use area of the battery 54 and is apredetermined temperature area of the battery 54 in which the chargeableand dischargeable powers Win and Wout do not decrease according to thebattery temperature THbat. With the electronic control unit 100including the condition determining unit 112, it is possible toappropriately prevent the engine rotation speed Ne from falling into ahigh-rotation state when the first rotary machine MG1 is subjected tothe predetermined output limitation. When the condition determining unit112 determines whether the vehicle condition is the predeterminedvehicle condition based on whether the first rotary machine MG1 issubjected to the predetermined output limitation, for example, a marginrotation speed difference calculation map in which the margin rotationspeed difference ΔNr is set to increase as the MG1 temperature THgdeparts farther from the predetermined normal temperature area THgra oras the battery temperature THbat departs farther from the predeterminednormal temperature area THbatra may be used instead of the marginrotation speed difference calculation map illustrated in FIG. 8 at thetime of calculating the margin rotation speed difference ΔNr.

For example, in the first embodiment, the condition determining unit 112determines whether the vehicle condition is the predetermined vehiclecondition based on whether the vehicle 10 is traveling on a road onwhich the driving wheels 16 are likely to slip. For example, thecondition determining unit 112 may determine whether the vehiclecondition is the predetermined vehicle condition based on whether thevehicle 10 is traveling on a road on which the driving wheels 16 arelikely to slip and whether the first rotary machine MG1 is subjected toa predetermined output limitation. When at least one of the conditionthat the vehicle 10 is traveling on a road on which the driving wheels16 are likely to slip and the condition that the first rotary machineMG1 is subjected to the predetermined output limitation is satisfied,the condition determining unit 112 is configured to determine that thevehicle condition is the predetermined vehicle condition.

In the decrease condition satisfaction determining unit 104 b accordingto the first embodiment, the supercharging pressure decrease conditionCD is satisfied when both the first condition CD1 and the secondcondition CD2 are satisfied. However, the supercharging pressuredecrease condition CD may be satisfied when only the second conditionCD2 is satisfied. That is, the supercharging pressure decrease conditionCD may be satisfied when the actual rotation speed difference ΔN isequal to or less than the margin rotation speed difference ΔNrregardless of whether the vehicle condition is the predetermined vehiclecondition which is determined by the condition determining unit 112.

In the decrease condition satisfaction determining unit 104 b accordingto the first embodiment, the margin rotation speed difference ΔNr isappropriately set, for example, using the margin rotation speeddifference calculation map illustrated in FIG. 8, but, for example, apreset one margin rotation speed difference ΔNr may be normally used.

In the first embodiment, when the assist possibility determining unit106 b determines that the shortage of the engine torque Te with respectto the required engine torque due to the decrease in the superchargingpressure Pchg by the supercharging pressure decreasing unit 104 a is notable to be compensated using the MG2 torque Tm of the second rotarymachine MG2, the torque compensation unit 106 a does not compensate forthe shortage of the engine torque Te using the MG2 torque Tm of thesecond rotary machine MG2. For example, even when the assist possibilitydetermining unit 106 b determines that the shortage of the engine torqueTe is not able to be compensated using the MG2 torque Tm, the torquecompensation unit 106 a may output the MG2 torque Tm which can be outputfrom the second rotary machine MG2 to compensate for a part of theshortage of the engine torque Te with respect to the required enginetorque due to the decrease in the supercharging pressure Pchg.

In the second embodiment, the condition determining unit 112 determineswhether the vehicle condition is the predetermined vehicle conditionbased on whether the vehicle 200 is traveling on a road on which thedriving wheels 206 are likely to slip. For example, the conditiondetermining unit 112 may determine whether the vehicle condition is thepredetermined vehicle condition based on whether the stepped gearshifting unit 218 which is an automatic transmission is subjected to agear stage limitation. The gear stage limitation refers to limiting thegear stage of the stepped gear shifting unit 218 to a low gear stagesuch that the temperature of an oil which is used for the stepped gearshifting unit 218 increases by increasing the rotation speed of anintermediate transmission member 228 which is an input rotary member ofthe stepped gear shifting unit 218 when the oil temperature is low. Whenthe oil temperature is low, controllability of gear shifting controlwhich is performed in the stepped gear shifting unit 218 deteriorates.When the stepped gear shifting unit 218 is subjected to the gear stagelimitation, the gear stage of the stepped gear shifting unit 218 islimited to a low gear stage and thus the engine rotation speed Ne islikely to increase.

In the first embodiment, the vehicle 10 may be a vehicle which does notinclude the gear shifting unit 58 and in which the engine 12 isconnected to the differential unit 60 like the vehicle 200. Thedifferential unit 60 may be a mechanism in which a differentialoperation can be limited by control of a clutch or brake connected tothe rotary elements of the second planetary gear mechanism 82. Thesecond planetary gear mechanism 82 may be a double pinion type planetarygear unit. The second planetary gear mechanism 82 may be a differentialmechanism including four or more rotary elements by connection between aplurality of planetary gear units. The second planetary gear mechanism82 may be a differential gear mechanism in which the first rotarymachine MG1 and the drive gear 74 are connected to the pinion which isrotationally driven by the engine 12 and a pair of bevel gears engagingwith the pinion, respectively. The second planetary gear mechanism 82may be a mechanism with a configuration in which some rotary elements oftwo or more planetary gear units are connected to each other and theengine, the rotary machine, and the driving wheels are connected to therotary elements of such planetary gear units in a power-transmittablemanner.

In the second embodiment, the one-way clutch F0 is exemplified as a lockmechanism that can fix the carrier CA0 in a non-rotatable manner, but anapplicable embodiment of the present disclosure is not limited to theaspect. This lock mechanism may be an engagement device such as anengaging clutch, a hydraulic frictional engagement device such as aclutch or a brake, a dry engagement device, an electromagneticfrictional engagement device, or a magnetic powder type clutch whichselectively connects the connection shaft 226 and the case 214.Alternatively, the vehicle 200 does not have to include the one-wayclutch F0.

In the second embodiment, the stepped gear shifting unit 218 isexemplified above as the automatic transmission constituting a part ofthe power transmission path between the differential mechanism 230 andthe driving wheels 206, but an applicable embodiment of the presentdisclosure is not limited to the aspect. The automatic transmission maybe an automatic transmission such as a synchromesh parallel biaxialautomatic transmission, a known dual clutch transmission (DCT) with twoinput shafts as the synchromesh parallel biaxial automatic transmission,or a known belt type stepless transmission.

In the first embodiment described above, a mechanical pump typesupercharger that is rotationally driven by an engine or an electricmotor may be provided in addition to the exhaust turbine typesupercharger 18.

The above-mentioned embodiments are merely exemplary and the presentdisclosure can be embodied in various aspects which have been subjectedto various modifications and improvements based on knowledge of thoseskilled in the art.

What is claimed is:
 1. A control device for a hybrid vehicle includingan engine with a supercharger, a first rotary machine that is able toadjust a rotation speed of the engine, and a second rotary machine andusing the engine and the second rotary machine as drive power sources,the control device comprising: a high rotation curbing control unitconfigured to control the engine and the first rotary machine such thatan operating point of the engine reaches a target operating point and tocontrol the engine such that an output torque of the engine decreaseswhen the rotation speed of the engine exceeds the maximum rotationspeed, the target operating point being set such that the rotation speedof the engine is within a range which does not exceed a maximum rotationspeed with a margin of the rotation speed of the engine from apredetermined upper-limit rotation speed of each of the engine and thefirst rotary machine and an output required for the engine is outputfrom the engine; a supercharging pressure decreasing unit configured todecrease a supercharging pressure from the supercharger when a speeddifference between the maximum rotation speed and the rotation speed ofthe engine is equal to or less than a set margin speed difference; and atorque compensation unit configured to compensate for a shortage of theoutput torque of the engine with respect to a required engine torque dueto a decrease in the supercharging pressure by the superchargingpressure decreasing unit using a second rotary machine torque of thesecond rotary machine.
 2. The control device for a hybrid vehicleaccording to claim 1, wherein the supercharging pressure decreasing unitis configured to decrease the supercharging pressure when the shortageof the output torque of the engine with respect to the required enginetorque is not able to be compensated for using the second rotary machinetorque and the speed difference is equal to or less than the marginspeed difference.
 3. The control device for a hybrid vehicle accordingto claim 2, wherein the supercharging pressure decreasing unit isconfigured to set an amount of decrease of the supercharging pressure bythe supercharging pressure decreasing unit to be less when the shortageof the output torque of the engine with respect to the required enginetorque is not able to be compensated for using the second rotary machinetorque than when the shortage of the output torque of the engine withrespect to the required engine torque is able to be compensated forusing the second rotary machine torque.
 4. The control device for ahybrid vehicle according to claim 1, further comprising a conditiondetermining unit configured to determine whether a vehicle condition isa predetermined vehicle condition in which the rotation speed of theengine is likely to exceed the maximum rotation speed, wherein thesupercharging pressure decreasing unit is configured to decrease thesupercharging pressure when it is determined that the vehicle conditionis the predetermined vehicle condition and the speed difference is equalto or less than the margin speed difference.
 5. The control device for ahybrid vehicle according to claim 4, wherein the condition determiningunit is configured to determine whether the vehicle condition is thepredetermined vehicle condition based on whether the hybrid vehicle istraveling on a road on which driving wheels to which power of the engineis transmitted are likely to slip.
 6. The control device for a hybridvehicle according to claim 4, wherein the condition determining unit isconfigured to determine whether the vehicle condition is thepredetermined vehicle condition based on whether the first rotarymachine is subjected to a predetermined output limitation.